Pass empty category string for internal Supermarket compatibility.
Pass empty category string for internal Supermarket compatibility.

Categories are optional both in knife cookbook site
(which this plugin seeks to replace) and on the
Supermarket community site.  Best practice now
seems to be to pass an empty string.

For more info, see:
https://github.com/chef/supermarket/pull/915
https://github.com/chef/chef/pull/2198

david-crowder/knife-supermarket,chef/knife-supermarket,gjmoed/knife-supermarket